Development of a two zone turbulence model and its application to the cycle-simulation

Abstract

The development of a two zone k-e turbulence model for the cycle-simulation software is presented. The in-cylinder turbulent flow field of internal combustion engines plays the most important role in the combustion process. Turbulence has a strong influence on the combustion process because the convective deformation of the flame front as well as the additional transfer of the momentum, heat, and mass can occur. The development and use of numerical simulation models are prompted by the high experimental costs, lack of measurement equipment and increase in computer power. In the cycle-simulation codes, multi zone models are often used for rapid and robust evaluation of key engine parameters. The extension of the single zone turbulence model to the two zone model is presented and described. Turbulence analysis was focused only on the high pressure cycle according to the assumption of the homogeneous and isotropic turbulent flow field. Specific modifications of differential equation derivatives were made in both cases (single and two zone). Validation was performed on two engine geometries for different engine speeds and loads. Results of the cycle-simulation model for the turbulent kinetic energy and the combustion progress variable are compared with the results of 3-D computational fluid dynamics simulations. Very good agreement between the turbulent kinetic energy during the high pressure cycle and the combustion progress variable was obtained. The two zone k-e turbulence model showed a further progress in terms of prediction of the combustion process by using only the turbulent quantities of the unburned zone.

Cycle-simulation turbulence modelling of IC engines

“…Schematic of a ECFM-3Z model computational cell (Colin and Benkenida, 2004). the turbulent kinetic energy of the unburned zone assuming the homogeneous and isotropic turbulent flow field (Ramos, 1989;Sjerić et al, 2014).…”

“…Although the cycle-simulation results of turbulent kinetic energy depended on the initial conditions specified at the IVC (Intake Valve Closure), very good agreement of turbulent kinetic energy over different engine operating conditions was obtained (Sjerić et al, 2012). The extension of the developed single zone turbulence model into a two zone model during the combustion process is presented and described in (Sjerić et al, 2014). The research presented in this paper aims to eliminate the necessity for specifying the initial conditions of turbulence at IVC and to close the loop in the turbulence simulation model by extending the calculation to the gas exchange process.…”

Towards better correlation between optical and commercial spark ignition engines through quasi-dimensional modeling of cycle-to-cycle variability

“…Such approaches feature a good compromise between accuracy and computational effort [7]. They are not as fast as ANN based models [8] but can ensure acceptable fastrunning characteristics [9] and several levels of detail can be implemented for augmenting predictive capabilities [10,11]. Data recorded on optically accessible units can ensure a solid starting point for model development and validation, as they feature high spatial resolution [12,13].…”

Modelling of early flame kernel growth towards a better understanding of cyclic combustion variability in SI engines

“…For the study specific modifications and extensions of the available fractal combustion model are made. For the modelling of in-cylinder turbulence a new turbulence model is implemented [26,27], while the combustion process is simulated by the modified fractal model that includes an ignition sub-model, a sub-model for transition from laminar to turbulent flame and a two zone turbulence sub-model. The early flame kernel growth is modelled by a newly [28] commonly used in 3D-CFD simulations.…”

“…In this study, the cyclic variability of combustion in SI engines is produced by a predefined perturbation of the turbulence intake production parameter, by a perturbation of the flow direction at the spark plug and by a perturbation of the stratification of air equivalence ratio from cycle-to-cycle, simulating the fluctuations of in-cylinder turbulence level, fluid motion and stratification of fuel, respectively. Since the combustion and turbulence models have already been described in previous publications [26,27], the description of the numerical model in this paper will be limited to the quasi-dimensional ignition model and to the methodology of inducing CCV in the simulations.…”